Hydroforming is a metal forming process through which metal tube blanks are formed into shapes, such as automotive body components, through the application of internal water hydraulic pressure.
Standard hydroforming techniques start with a sheet of metal or a bent tube. Hydroforming differs from conventional deep drawing processes by replacing die tools with rubber diaphragms, which are backed with fluid pressure, to form punch tool components.
Relating the aforementioned concept to tubular parts, a tube is placed in a die, then the tube is filled with a fluid pressure to form a part to the die. In other words, the tube blanks are reshaped through cross-sectional changes along the length of the tube blanks.
Low pressure sheet forming, through which the tube is filled with a low pressure fluid that forms the part to the die, is ideal for parts with large radii, simple cross sections, and flat surfaces. High pressure sheet forming is ideal for parts requiring complex cross sections with small radii. The drawback to high pressure forming is that, due to friction, parts tend to have non-uniform thickness.
For active hydroforming, the part is placed in the hydroforming press. Before the press is cycled shut, a fluid pressure is applied to expand the part while maintaining the metal at a uniform thickness. The resulting part tends to have uniform thickness even for complex cross sections. Active hydroforming takes the strong points from high and low pressure hydroforming and combines them into a single process.
The hydroforming process allows close control of parameters (e.g. fluid pressure and lubrication) to prevent wrinkling and tearing of parts. High quality parts that are substantially hard, resistant to buckling and unlikely to have surface defects are produced through hydroforming. Improved process flow also tends to result from decreased die wear due to fluid on metal forming rather than metal on metal forming.
Hydroforming flows metal rather than stretching it. Therefore, thinning of material is minimal. This often results in material savings because thinner blanks can be used, which is an important factor in decreasing costs when expensive alloys are required or a large number of parts are ordered.
The existing stamped shape of a front rail for a unitized body has the end that the bumper attaches to flared open initially and gradually decreased in cross sectional dimensions as the rail bypasses the tire envelope on one side and powertrain on the other side. Once past the tire envelope and powertrain, the section is again increased in cross sectional dimensions as it transitions to the dash. Replacing the front stamped rail with a regular tube shape hydroformed rail requires end feeding into a hydroform press to get expansion near the ends during a hydroforming process, and this method of feeding tends to limit the degree of conical shape, which is needed for automobile body engineering requirements.
The limitation associated with current component molding techniques has made it apparent that a modified technique to mold components is necessary. The modified technique should substantially minimize steps required for a hydroforming process and should facilitate compliance with automobile body engineering requirements. The present invention is directed to these ends.